The present disclosure relates to a transmission control device, a transmission control method, and a transmission control program.
A procedure called three-way handshaking has been known as the procedure for establishing a socket-to-socket connection under the transmission control protocol (TCP), the connection being known as the TCP connection.
In three-way handshaking, a client requesting communication with a server transmits a synchronize (SYN) packet to the server, for example. On receiving the SYN packet, the server transmits a synchronize-acknowledge (SYN+ACK) packet to the client. Upon receipt of the SYN+ACK packet, the client transmits to the server an acknowledge (ACK) packet and transmission target data such as a hypertext transfer protocol (HTTP) request. In this manner, the transmission target data is transmitted from the client to the server. The time required for the client to transmit the SYN packet to the server and to receive the SYN+ACK packet from the server is called a round-trip time (RTT) in three-way handshaking.
The request for comments (RFC) 7413 describes the technique called TCP fast open (TFO) as a typical technique for speeding up TCP-based communication related to three-way handshaking.
The TFO involves having a TCP option included in the SYN packet transmitted from the client to the server in three-way handshaking, the TCP option indicating that the TFO is enabled. The server supporting the TFO and having received the SYN packet transmits to the client the SYN+ACK packet including data called cookies. Upon receipt of the SYN+ACK packet, the client transmits the ACK packet and transmission target data to the server.
Thereafter, when communication between the same sockets is resumed, the client transmits to the server the SYN packet that includes the cookies previously received from the server and the transmission target data. The TFO thus allows the client having received the cookies from the server to transmit the transmission target data to the server without waiting for the receipt of the SYN+ACK packet in three-way handshaking. This eliminates the communication time corresponding to one RTT in three-way handshaking, thereby improving communication rate.